Importing image with original asspect ratio without cropping
You have found right option, the only thing left is to animate it.

With your credits imported, find the best Offset options (both X and Y) to make them begin the credits being in the bottom and end - in the top of frame, and animate your found values:



So, in the 1st frame this value is -1850 for me, and in the last - around 230. 

The result will be scrolling your text:



text from here

The much more in-depth solution is provided in this solution